1. Field of the Invention
This invention relates to a monoaxial coarse and fine adjusting mechanism for an optical instrument such as a microscope.
2. Description of the Prior Art
Generally, the focusing requirements of precision instruments such as microscopes require both a coarse adjusting mechanism and a fine adjusting mechanism. The coarse adjusting mechanism allows the operator to rapidly raise or lower the stage or nosepiece assembly to roughly bring the specimen being viewed into focus. The fine adjusting mechanism is then rotated to bring the specimen into sharp focus.
It is common to have such coarse and fine adjusting mechanisms coaxially mounted. Although these mechanisms are coaxially mounted to each other, they operate independently of each other. That is, rotation of the coarse adjusting knob would rotate a coarse adjusting shaft which is mechanically connected directly to, for instance, a stage mechanism by a rack and pinion assembly. Rotation of the knob, therefore, causes gross movement of the stage mechanism. However, when the fine adjusting knob is rotated, it rotates a fine adjusting shaft that in turn has direct mechanical connection to the stage mechanism which is separate and distinct from the coarse mechanism. In essence, although the coarse and fine adjusting mechanisms are coaxially mounted, two complete and separate adjusting mechanisms are required to accomplish coarse and fine adjustments.
Several efforts have been made which attempt to overcome the problems inherent in such dual adjusting mechanisms. However, these devices generally result in a mechanism which is difficult to manufacture and assemble and, accordingly, costly to produce.
One such attempt is shown by L. A. Wilkinson in U.S. Pat. No. 3,019,705 which issued Feb. 6, 1962. In this mechanism a monoaxial coarse-fine adjusting mechanism is shown which utilizes a single gear and rack to accomplish both coarse and fine movement. Rotation of the coarse knob transfers directly into coarse movement of the adjustable member, which in this instance is the stage. Rotation of the fine knob rotates an eccentric member which in turn rotates a spur gear. The spur gear meshes with a pair of sun gears one of which is mounted to the knob while the other is mounted to the adjusting shaft. The sun gears have different numbers of teeth. One of the sun gears is driven and one is held stationary. Due to the difference between those two gears the amount of fine movement may be controlled. However, this system requires gears which are costly to produce. Further, tolerances must be closely kept in order to produce desired results. Still further, this apparatus does not appear to have any provisions for removing backlash from the system.
A further coaxial coarse-fine adjusting mechanism may be found in U.S. Pat. No. 3,019,707 which issued Feb. 6, 1962 to H. W. Straat. The mechanism consists of a worm gear mounted to the coarse shaft which directly drives a pinion gear mounted to the stage mechanism. The fine shaft has a nut captured by the coarse worm gear. Rotation of the fine shaft moves the nut linearly such that fine adjustment can be made.
U.S. Pat. No. 3,768,885 issued Oct. 30, 1973 to O. W. Boughton et al discloses a further microscope focusing system. The coarse-fine focusing mechanism in this device comprises a movable nosepiece which is connected to a linkage that is in direct engagement with a rotatable cam. The cam is rotated by a reduction gear system in order to accomplish fine movement. The cam and the gear system are both rotated together to effect coarse movement. The reduction gear system is comprised of a plurality of gears and pinions enclosed in a gear box. The gears and pinions are expensive to manufacture and assemble. In order to function properly, the gears and pinions must have close tolerances. Accordingly, these necessities add to the complexity and cost of the final product.
Further coarse-fine adjusting systems may be found in U.S. Pat. Nos. 3,135,817 and 3,260,157. These systems feature compound cams and linkage. The cam would be directly rotated to accomplish coarse adjustment and axially translated for fine adjustment.